To evaluate in pts. w/ neurally-mediated syncope & normals, resting auto. funct. & reflex response of the auto. nerv. system to head-up tilt. We will test the hypothesis that many pts. w/ neurally-mediated syncope have an exaggerated auto. response to head-up tilt (w/ greater vagal withdrawal & sympathetic excitation). This will provide the 1st classification of pts. w/neurally-mediated syncope according to the autonomic mechanism responsible for the genesis of the disorder.